1. Field of the Invention
The present invention relates to molded resin foams.
2. Related Art
In the air conditioning system of an automobile or the like, for example, a tubular air conditioning duct for venting air is used. A known example of an air conditioning duct is a molded foam (hereinbelow referred to as “foam duct”) for which a resin foam is used consisting of a thermoplastic resin foamed by a foaming agent. Demand in foam ducts has grown because of their strong heat insulating properties and low weight.
A widely known example of a method for manufacturing such a foam duct is blow molding in which a melted resin is clamped in a divided mold and the interior is filled with air and then the air is expanded. With recent improvements in molding techniques, it has become possible to mass-produce foam ducts with increased expansion ratios.
A known example of a technique recently submitted for application by the applicant is a foam duct molded by foam blow molding in which a supercritical fluid is added as a foaming agent, wherein the surface roughness and expansion ratio on the outer surface are within a predetermined range (see Japanese laid-open patent publication No. 2005-241157, for example).